1. Field of the Invention
The present invention relates to a process and apparatus for producing metallic composite materials.
2. Description of the Prior Art
Conventional two- or three-layer metallic composite plates can be produced by preparing different metallic plates separately, cutting the plates to predetermined dimensions, combining the plates together, and pressure-bonding the plates by rolling or bonding them by an explosion technique. In accordance with this method, since different metallic plates are required to be produced separately and cut to predetermined dimensions prior to being bonded together, this method results in relatively low yield. In addition, the production steps are complicated, and the production costs are high.
In order to overcome the above-described problems, another method has been proposed and is now in practical use. In this method, a metallic plate is placed in a mold at a predetermined position, and a second metal in molten form is then poured into the mold in such a manner that the second metal surrounds the metallic plate to produce a metallic laminar composite material. Of course, the second molten metal has a different composition than the metal of the metallic plate.
FIG. 5 illustrates a prior art apparatus for making a metallic laminar composite material according to this latter method. In FIG. 5, a metallic plate 1 is covered with a surface coating agent to prevent oxidation of the surface of the metallic plate 1, and this plate is hung in a mold 13 which is made of cast iron. The mold 13 is covered at a predetermined position with a heat-insulating plate 12 which has a riser portion. A second, different molten metal is then introduced through an injection pipe 14 and a runner brick 15 and is charged into a clearance between the mold 13 and the metallic plate 1 to form a metallic laminar composite material. This method, however, suffers from the following disadvantages:
First, in order to eliminate various factors which inhibit efficient bonding between the metallic plate 1 and the second molten metal in a subsequent bonding processing step (for example, pressure-bonding by rolling), it is necessary to coat the surface of the metallic plate uniformly with a coating agent. The coating agent is required to prevent the surface of the metallic plate 1 from oxidizing when the second molten metal is poured into the mold 13, and it is also required to minimize the adverse effects caused by the introduction of scum which enters the mold as the molten metal is poured into the mold. Furthermore, not all coating agents will satisfactorily prevent oxidation from occurring or minimize the effects of scum, and the conditions under which the second molten metal is poured are required to be strictly controlled.
Second, to change the ratio in thickness of the metallic plate 1 and the second metal plate resulting from the different molten metal in the finished metallic laminar composite material, it is necessary to change either the thickness of the plate 1 or the thickness of the cast second plate. Therefore, depending on the dimensions of the articles to be produced, it is often necessary to employ different metal molds which have different dimensions.
Third, since the mold is made of cast iron, surface cracking of the second metal after it has been solidified is likely to occur, depending on casting conditions.
Fourth, in order to compensate for shrinkage as the second molten metal cools and solidifies, it is necessary to provide a riser over the entire mold head, and this leads to a reduction in yield.
Fifth, due to repeated castings, the surface of the mold tends to wear out over time, and the thickness of the second metal in the finished metallic laminar composite material becomes uneven. Accordingly, dimensional accuracy is reduced.